The disc brake is a brake for a wheel which slows down the rotation of the wheel by friction caused by pushing brake pads against a brake disc usually with hydraulic force. The brake disc rotates in unison with the wheel and/or the axle. To stop the wheel, friction material in the form of brake pads, mounted on a device called a brake caliper, is forced against both sides of the disc. The caliper can be forced by many different mechanisms including mechanically, hydraulically, pneumatically and/or electromagnetically. Friction causes the disc and attached wheel to slow or stop.
The brake disc, also known as the rotor, is the disc component that is attached to or rotates with the wheel against which the brake pads are applied. The disc is usually made of cast iron, but may also be made of steel, composites such as reinforced carbon-carbon, ceramic matrix composites, or other materials. Brake discs are all substantially disc shaped, but can vary in many aspects of their design. For example, some discs are simply solid through their thickness. Ventilated discs have vanes or voids between the opposing friction faces to improve cooling, which can be particularly important for heavy, high-speed, or high-power applications where much heat needs to be dissipated. As another example, some brake discs have holes drilled through the friction faces, known as cross-drilled discs. As yet another example, discs may also be slotted, where shallow channels are machined into the disc to aid in removing dust and gas. Slotted disc designs may be the preferred method in most racing environments to remove gas and water and to deglaze brake pads. Slotted discs may be beneficial to race vehicles because they keep the pads effective and avoid vitrification and other detrimental transformations of their surfaces. Discs are typically mounted on the wheel via studs. However, high performance discs may be mounted to a hat or mounting bell in a way that allows it to expand in a controlled symmetrical way with less unwanted heat transfer to the hub, thereby reducing and/or eliminating thermal stress, cracking and warping.
Brake pads are designed to transmit high friction forces while wearing evenly. Depending on the properties of the material of both the pad and the disc and the configuration and the usage, pad and disc wear rates will vary considerably. The properties that determine material wear involve trade-offs between performance and longevity. The brake pads must usually be replaced regularly (depending on pad material), and some are equipped with a mechanism that alerts drivers that replacement is needed. Generally, road-going vehicles have two brake pads per caliper, while up to six are installed on each racing caliper, sometimes with varying frictional properties in a staggered pattern for optimum performance.
Bedding, also known as burnishing, is a process using heat and/or friction to alter the surface of a brake pad and/or a brake disc. Bedding of brake pads and/or discs may be desired to improve the performance of a brake system. The formation of a transfer layer of brake pad friction material on the brake disc can raise the friction coefficient and/or make the friction level more consistent under a variety of speeds, pressures, and temperatures. The heat and mechanical working of the brake disc surface can also relieve stress within the brake disc reducing the likelihood of cracking of the brake disc when in use. As such, bedding or burnishing of the brake pads and discs is an important part of the preparation for brake pads and discs, particularly for those that will be exposed to severe conditions, like in the racing industry.
When bedding the brake pads and discs, the amount of transfer layer developed and stress relieved are both highly pressure and temperature dependent. Thus, bedding of the brake pads and discs requires a controlled process. Burnishing can be performed on the vehicle, however, there is seldom a way to measure and precisely control component temperature while driving. Lack of control can yield inconsistent results.
As a result, burnishing of brake discs and pads before installation on a vehicle is known to be performed on machines. The amount of control used with these machines with respect to temperature has been limited. Often an inertia wheel has been used by spinning it up to a specified speed, applying a braking force, and removing the brake pressure once the second specified speed is achieved or after a specified time interval. Alternatively, a driving device of some other form turns the brake disc and applies braking torque according to specified time intervals or durations. The problem with these techniques is that they cannot accurately control a desired peak temperature. In addition, these techniques can not hold the brake pad or brake disc surface within a small predetermined temperature range for long time periods.
The instant invention is designed to address the above mentioned problems by providing a machine and method for more accurately and consistently bedding brake discs and/or pads.